The subject matter disclosed herein relates generally to a method and system for communication in a motor drive application and, more specifically, to a method and system for providing network communications between a motor drive, a motor, and other end points connected to the motor drive.
Servo motors are one type of motor which are typically employed in applications that require precise positioning. Exemplary applications for servo motors include robotics, automated manufacturing, conveyor systems, pick and place machinery, computer numerical control (CNC) for precise machining, printing applications, and the like. Servo motors are commonly paired with a motor controller and a position feedback device where the servo motor controller may include algorithms paired with the motor and the position feedback device has high resolution to facilitate precise positioning.
Commonly, servo motors and motor controllers are incorporated into a larger controlled machine, system, or process. The controlled machine, system, or process may include a central controller, one or more distributed industrial controllers, and often multiple servo motors and motor controllers. The central controller may be a desktop computer located in a control room or in a remote facility. Optionally, the central controller may be an industrial computer, configured to operate in a harsh environment and located at the controlled machine, system, or process. The industrial controllers include processors and operating systems optimized for real-time control and are programmed with languages designed to permit rapid development of control programs tailored to a constantly varying set of machine control or process control applications.
An industrial control network is typically employed to facilitate communications between devices in the controlled machine, system, or process. The industrial networks are typically selected to exhibit highly reliability and real-time communication. The industrial network may utilize protocols such as EtherCAT®, Ethernet/IP®, or Profinet® which have been developed for automation applications and include features such as a guaranteed maximum communication delay, low communication jitter, pre-scheduling of the communication capacity of the network, and/or providing seamless redundant communication capabilities for high-availability.
Historically, it has been known to install the network between controllers, such as the central controller and the industrial controller. Further, certain devices such as motor drives may be configurable, include a large parameter set, have sufficient processing capabilities, or the like such that they may include a network interface and are also connected to the industrial network. Other devices, however, such as motors, sensors, relays, and other actuators, provide input signals to or receive output signals from one of the controllers and perform fixed tasks in the controlled machine, system, or process. These devices are typically located remotely, and often at long runs, from the control cabinets in which the controllers are located. Wiring must be run between the control cabinets and each of the device. Because of the expense of running network cabling to and providing network interfaces on every device, many of these devices are not connected directly to the network. The input and/or output signals are transmitted directly between one of the controllers and the device. Optionally groups of signals may be routed to an intermediate location and pass through a gateway which is connected to the industrial network and which can convert the input and output signals from separate signals to data in a message packet to be transmitted via the desired industrial protocol for at least a portion of the distance between the controllers and the devices.
Traditionally, a motor controller has served as a gateway in the industrial network. The motor controller includes a network interface and is configured to communicate via the industrial network. The motor controller also communicates on a point-to-point basis to transmit and receive output and input signals with devices connected to the motor controller. The devices include, for example, a brake on the motor, or a temperature sensor, or a position encoder mounted on the motor.
However, recent trends have been to include additional sensors on the motor to monitor operating conditions in the motor. The additional sensors may include, for example, vibration sensors mounted to the motor as disclosed in U.S. Pat. No. 9,673,685 to measure the vibration present on the motor. Temperature sensors may be mounted at different locations on the motor and/or encoder to provide information on ambient conditions or to provide early detection of an impending failure in the motor.
The addition of additional devices communicating with the motor controller introduces an additional burden on the resources of the motor controller. The communications interfaces must process additional signals. Further, different communications protocols may be utilized by different devices, requiring the motor controller to be able to accept each of the communication protocols. Certain communications are unidirectional, providing, for example, data from a sensor to the motor controller, but preventing, for example, configuration of the sensor by the motor controller. For devices that allow bidirectional communication with the motor controller, the communication is restricted to configuration data and does not provide for control of the device over the network. Further, increasing complexity and more demanding performance requirements for control routines to control operation of the motor place competing demands on the resources of the motor controller.
Thus, it would be desirable to provide an improved method and system for communication among devices connected to a motor controller in a motor drive application.